If you are arriving at the International airport(EZE), then there will be transportation kiosks after the customs Xray. Look to your left and 3 companies(World,VIP,TiendaLeon) have private cars directly to your hotel. In addition, in the Arrivals Hall is the kiosks for TAXIEZE. The 3 private car companies take both cash(Dollars,pesos,Euros) or credit cards. TAXIEZE takes the same cash only. The price to your hotel is 180-210 pesos. There is also an airport shuttle from TiendaLeon which costs 50 pesos to their downtown terminal but requires a taxi transfer to your hotel.
Do not go outside the terminal and arrange for your own taxi at the curb.
If you are changing your currency to pesos then use only Banco de la Nacion at the airport. They offer the best exchange rate and located next to the car companies.
There is also an ATM in this area of the airport which dispenses pesos.
There is a maximum of 1000 pesos per transaction with a local charge of 17pesos. However, you can withdraw more pesos by reinserting the ATM card but pay again the local charge.